Description (Adapted from application): Sexually active adolescents are at increased risk for sexually transmitted diseases (STDs). The introduction of DNA tests, which utilize non-invasive samples such as urine, have greatly increased the number of STD infections detected, thus the tools to biologically monitor (biomarkers) interventions, which previously have been measured by self-report, are now available clearly documenting high prevalences of infections with C. trachomatis, N. gonnorrhoeae, and T. vaginalis Sequelae of these asymptomatic infections are serious and costly. Interventions to reduce exposure to these agents by changing sexual risk behaviors are greatly needed. In this study, a successful safe-sex intervention "Focus on Kids" will be modified for use in high schools, and administered during lunch periods to approximately 1,350 ninth grade adolescents in five inner-city schools with School Based Health Centers (SBHC). Students, sexually active or not, will be invited to participate in this intervention study which will be advertised broadly at the beginning of the school year. Sexually active students participating in the intervention will be actively enrolled in the biomarker portion of the study in the SBHC and undergo screening for chlamydia, gonorrhea and trichomonas twice a year. Symptomatic students would also be screened as per clinical protocol. Baseline and self-reported behavior changes resulting from the intervention will be evaluated by questionnaire at the beginning and end of the intervention, and at 6- months and at 12-months following completion of the intervention. All students found to be infected will be treated appropriately. Self-reported behavior changes, both short and long-term, will be correlated with biomarker results. The relationship of clinical and demographic variables to biomarkers will be determined, and the relationship and effect of sexual mixing patterns on prevalence of STDS will also be determined. This multi-disciplinary and cooperative study encompassing behavioral, interventional, epidemiological, and biological sciences will evaluate a behavioral approach to STD prevention and control.